Process of electrolytic pickling of copper-beryllium alloys

ABSTRACT

A PROCESS FOR PICKLING PART FORMED OF COPPER-BERYLLIUM ALLOY IN WHICH SMALL AMOUNTS OF NICKEL OR COBALT MAY BE PRESENT AS ADDITIONAL ALLOYING ELEMENTS, WHEREIN THE PART TO BE PICKLED IS CONNECTED TO THE ANODE IN A DIRECT CURRENT ELECTROLYSIS CELL IN WHICH THE ELECTROLYTE IS AN AQUEOUS SOLUTION OF AN ALKALI METAL HALIDE PRESENT IN AN AMOUNT WITHIN THE RANGE OF 100-200 GRAMS PER LITER AND A SURFACE ACTIVE AGENT.

United States Patent Int. 01. C23b 1/00 US. Cl. 204141 7 Claims ABSTRACTOF THE DISCLOSURE A process for pickling parts formed ofcopper-beryllium alloy in which small amounts of nickel or cobalt may bepresent as additional alloying elements, wherein the part to be pickledis connected to the anode in a direct current electrolysis cell in whichthe electrolyte is an aqueous solution of an alkali metal halide presentin an amount within the range of 100-200 grams per liter and a surfaceactive agent.

This invention relates to the process for pickling beryllium containingcopper alloys and it relates not only to copper alloys containing 1.8-2%beryllium but also to such alloys which may contain small amounts ofnickel and/or cobalt and to ternary alloys containing 0.4 to 0.7%beryllium, 1.2-2.5 nickel or 2.3 to 2.7% cobalt.

Semifinished products, sheets, strips, wires and the like which areformed of such alloys are usually subjected to thermal treatmentswhereby an oxide layer forms on the surfaces, notwithstanding theprecautions which might be taken to avoid surface oxidation. Eliminationof such oxide layer is difficult and removal is effected by a picklingoperation.

Pickling becomes increasingly difficult at increasing temperature. It isfor this reason that it is difficult to pickle ternary alloys of thetypes described having a relatively high cobalt or nickel content byintroduction into a pickling solution at a temperature of about 900 C.

Two techniques are employed generally for pickling copper-berylliumalloys. In one system, pickling is carried out in an aqueous solutioncontaining 20-50% by volume sulphuric acid. The operation is carried outat a temperature within the range of 40-60 C. by immersion for 10-60minutes, depending somewhat on the degree of oxidation. After rinsingwith water, the part is immersed for a few seconds in achromatosulphuric mixture containing 50 g. chromic acid and 150 cc. ofsulphuric acid (66 B.) in 850 g. of water. This process is slow and thetreated surface has an irregular appearance. With alloys of copper,cobalt and beryllium, pickling is not complete.

In the other system, also a chromatosulphurie pickling process, theoperation is carried out at a temperature within the range of 40-70 C.in a bath containing 50 g. chromic acid and 150 cc. sulphuric acid (66B.) in 850 g. of water. Treatment is effected for one minute to producea satisfactory surface even with copper-cobaltberyllium alloys.Unfortunately, the process is troublesome because the bath deterioratesrapidly by reason of the reduction of the chromic acid in the bath.

It is an object of this invention to provide a method and means forremoval of oxides from the surfaces of copper-beryllium alloys of thetypes described by a pickling process which is safe and efficient andwhich gives good results from the standpoint of appearance and surfacefinish, and in which the desired pickling process can be carried outwithout difficulty and in a short space of time.

In accordance with the practice of this invention, the usual chemicalpickling process is replaced by an electrolytic pickling process inwhich use is made of an aqueous electrolyte solution containing at leastone alkali metal halide and a surface active agent. The process of thisinvention is applied to the cleaning of copper-beryllium alloys havingan oxide layer, such as the type produced during thermal treatment ofthe alloy, even when carried out in an inert atmosphere.

The following will list some of the principal advantages of the processof this invention. Pickling can be carried out rapidly, the treatment isapplicable to ternary alloys containing up to 2.7% cobalt or nickel aswell as to alloys containing 1.8-2% beryllium with a small amount ofcobalt or nickel; it gives a fine and uniform metallic appearance to thepickled parts; and it is capable of continuous operation as well asbatch operation and it makes use of an electrolyte formulated of readilyavailable, low cost materials thereby to provide an inexpensive andeconomical pickling process.

In a preferred practice of this invention, the metal to be pickled isconnected to the anode of a direct current generator while the cathodeis an inert conductor, such as stainless steel. The electrolysis bath isformulated of a solution of sodium chloride in water with a surfaceactive agent to assist in the removal of the greyish black oxide whichforms as a deposit during pickling. The wetting agent releases thedeposit for removal.

The concentration of materials making up the electrolyte and theoperating conditions, such as current density, can be varied over fairlywide limits. For example, the concentration of sodium chloride or otheralkali metal halide can be varied within the range of and 200 g. perliter. The pH of the bath can vary within the range of 5.5 to 8.5 andthe temperature of the bath can be varied within the range of 25-45 C.The voltage at the terminals is of the order of about 2 volts with acurrent density within the range of 3-5 amperes per square decimeter.

As the wetting or surface active agent, use can be made of an alcohol ora commercial wetting agent such as an anionic, cationic or nonionicsurface active agent which is compatible with the pH of the bath andwhich are of the type described in Oil and Soap, vol. XVII, No. 9,September 1941 (pages 179-182), by Harris, Epstein & Kohn. The amount ofwetting agent depends upon its composition. If an alcohol is used, suchas ethanol or methanol, the amount employed should be within the rangeof 50- 100 g. per liter. In the event that use is made of a commercialsurface active agent, the amount generally employed is within the rangeof 1-5 g. per liter.

The pickling treatment can be varied from 2-15 minutes dependingsomewhat on the thickness and character of the oxide layer on the metalsurface. After pickling, the part is rinsed with water to removeelectrolyte and then dried.

The following examples are given by way of illustration, but not by wayof limitation, of the practice of this invention:

EXAMPLE 1 Strips of copper-beryllium alloy having 1.9% by Weight ofberyllium and 0.3% by weight of copper, tempered in an inert atmospherehad an oxidized surface following tempering treatment. The strips werepickled by electrolysis in an aqueous bath containing 200 g. per litersodium chloride and 77 cc. per liter methanol.

The cathode was formed of stainless steel plate and the strip of metalwas connected to the anode and passed through the electrolytic bath at aspeed such that the residence time in the electrolyte was 3 minutes. Thevoltage at the terminalswas 2 volts and the current density was amperesper square decimeter.

Upon removal from the bath, the strip was rinsed in clean running waterand dried, and the metallic appearance obtained was very uniform.

EXAMPLE 2 The elements, consisting of copper-cobalt-beryllium alloy,having 2.5% by weight cobalt and 0.5% by weight of beryllium, wereoxidized during thermal treatment and suspended from the anode forimmersion in a bath containing 150 g. per liter sodium chloride and 2 g.per liter Celanol A (a neutral polyethoxyether surface active agent).

Pickling was continued for minutes at 35 C. with a terminal voltage of 2volts and current density of 5 amperes per square decimeter. Theelements Were removed and rinsed in clean running water and dried. Acomplete and very regular pickling was obtained which gave a uniformappearance to the metal surface.

The metal halides and other surface active agents may be employed in theprocesses of Examples 1 and 2 without departing from the spirit of theinvention, and other changes may be made in the details of formulationand operating conditions without departing from the spirit f theinvention, especially as defined in the following claims.

I claim:

1. A process for pickling copper based alloys including at least 0.4%beryllium and up to 2.5% nickel or up to 2.7% cobalt, comprising thesteps of connecting the alloy with the anode in a direct currentelectrolysis bath in which the bath consists essentially of an aqueoussolution of an effective amount of a salt supplying chloride ions and asurface active agent, adjusting the pH of the bath to a value within therange of 5.5 to 8.5, and applying an electrical current between theanode and cathode at a current density which does not effect metalremoval and while maintaining the bath at a temperature within the rangeof from about C. to about 45 C.

2. The process as claimed in claim 1 in which the chloride salt issodium chloride.

3. The process as claimed in claim 1 in which the chloride salt ispresent in the dissolved state in the bath in an amount within the rangeof 100-200 g. per liter.

4. The process as claimed in claim 1 in which the surface active agentis an alcohol present in an amount within the range of 50-100 g. perliter.

5. The process as claimed in claim 1 in which the surface active agentis selected from the group consisting of an anionic, cationic andnonionic surface active agent present in an amount within the range ofl-5 g. per liter.

6. The process as claimed in claim 1 in Which the electrolytic bath hasa pH within the range of 5.5-8.5 and is maintained at a temperaturewithin the range of 20-45 C. during pickling.

7. The process as claimed in claim 1 in which the pickling is carriedout by passing a current density of 3-5 amperes per square decimeterthrough the cell with the alloy connected to the anode.

References Cited UNITED STATES PATENTS 3,058,895 10/1962 Williams204-143 OTHER REFERENCES ROBERT K. MIHALEK, Primary Examiner

